Kevin Nunes murder: Detective had affair with another officer on the case

DC Nigel Sargeant even met the woman at a 'safe house' where the key witness was being kept.

But, incredibly, the affair was never revealed to the jury at the trial of five men who were convicted of killing the small-time gangster in a South Staffordshire country lane.

They later had their convictions quashed after serious police failings were exposed by a whistleblower.

A report into the scandal – codenamed Operation Kalmia – was completed two years ago this weekend in 2014, but has still not been made public.

Meanwhile, a number of officers in the case – including Mr Sargeant – have retired.

He has since worked for the Brighter Futures sexual exploitation service in North Staffordshire. He was approached for comment but has so far not responded.

Mr Sargeant was one of the main handlers of star witness Simeon Taylor in the Nunes case.

Court papers obtained by the Express & Star, which refer to Mr Sargeant as DC Nigel, state: "DC Nigel, one of the handlers of Simeon Taylor, was having an affair with the disclosure officer. They met where Simeon Taylor was being housed.

"Its potential impact is obvious. Had it been disclosed it could have been utilised by the defence to prove that Simeon Taylor's knowledge of the circumstances of the offence had not been acquired by being present when the offence was committed but by having information passed to him by someone handling him."

It adds: "It is of note that when Simeon Taylor gave evidence he said he knew that the inquiry team had no forensic evidence. He was unable to say how he knew that."

The potential impact of the affair was one of the provisional submissions made by defence lawyers appealing the murder convictions.

Senior Treasury Counsel Mr Richard Whittam QC, in his note to the Court of Appeal, said the prosecution at the original murder trial had made 'powerful points' about how Simeon Taylor's evidence could be relied upon.

But he added: "However the validity of this argument must now be doubted in light of the affair between the disclosure officer and DC Nigel.

"It is a feature of Simeon Taylor's evidence that he knew of the detail of the prosecution case such as the absence of cell-site or forensic evidence: the disclosure officer was visiting where he was housed and in an intimate relationship with an officer responsible for his welfare. Although there is no evidence information was actually passed, that relationship should have been disclosed and would have been utilised."

Police bosses knew about the affair a year before the original case went to trial.

It was documented in a secret police internal investigation culminating in the Costello Report, which the Express & Star has been fighting to obtain through Freedom of Information law.

Extracts from the report are quoted in the court papers obtained after an investigation by this newspaper spanning three years.

In respect of the disclosure officer staying where DC Nigel was meeting Simeon Taylor the report states: "...had there been an admission or evidence that she had met Simeon Taylor her position as disclosure officer would have been untenable."

It adds: "Having taken into consideration the importance and sensitivity of the prosecution case and the position these officers held within the inquiry their conduct can only be considered as totally irresponsible."

The Costello Report recommended that Mr Sargeant be excluded from handling witnesses and informants and that he receive 'formal advice' about meeting the disclosure officer whilst on protected witness duties.

According to the court papers, the report went on to state there were 'significant concerns about the objectivity, judgment, and overall professionalism' of DC Sargeant.

Mr Nunes, an amateur footballer from Wolverhampton, was shot in an execution-style killing in a Pattingham country lane in 2002. Five men were jailed in 2008 for life but their convictions were quashed in 2012 after serious police failings came to light.

A report by the police watchdog, which investigated 14 Staffordshire officers, has not been published despite being completed two years ago.

Deputy Chief Constable, Nick Baker said: "As the Independent Police Complaints Commission (IPCC) has undertaken a long and detailed inquiry into Operation Kalmia. We currently await publication, which is solely the responsibility of the IPCC.

"Until then, it is inappropriate for Staffordshire Police to comment further on specific questions. It should be noted that Kalmia was reviewed by the Crown Prosecution Service which concluded that none of the officers involved should face any criminal charges."